Manufacturing of a product or assembly of some apparatus generally involves the handling of work-pieces, for example components to be assembled. In particular, these work-pieces need to be transported between different locations, like assembly stations, inspection stations, packaging stations, or transport means as they proceed through the manufacturing process. In modern automated or semi-automated manufacturing, such handling of work-pieces is usually done by robots. A large number of components may be handled in parallel. For example, electronic components are often transported in molded matrix carriers, for example JEDEC trays. The electronic components are situated in the pockets, or cells, of the trays. Placing components into the pockets or picking components from the pockets for transferring them to a different location, i.e. for inspection or assembly, is usually done by pick-and-place robots. A pick-and-place robot typically comprises one or several so-called grippers (or pickers) that can pick-up an electronic component from a pocket of a tray and also place an electronic component into a pocket of a tray. The gripper may be mechanically clamping the electronic component or, more commonly, be using vacuum nozzles.
In order to increase throughput, pick-and-place robots are often equipped with multiple grippers such that several components can be picked up or placed in parallel. Common configurations are pick-and-place heads that have enough grippers to pick up an entire row of components at the same time or in some cases two entire rows of components at the same time.
In a typical manufacturing process most pockets of a tray contain one component that can be picked up by a gripper. There are, however, usually also a few pockets per tray that are empty or pockets that contain an incorrectly placed component, e.g. tilted or rotated. From such pockets no components can be picked up and a vacuum nozzle that is placed above such a pocket will not attain vacuum. Conventional multi-nozzle/gripper pick-and-place robots using vacuum nozzles have therefore independent/individual vacuum/blow-off supply lines along with individual vacuum sensors for each nozzle such that if there is a nozzle at an empty pocket or at an incorrectly placed component, where no vacuum can be attained, other nozzles will not be affected but can pick up components by vacuum, hence, operate correctly.
That means that in order to increase the number of grippers or nozzles, the number of vacuum supplies and of vacuum sensors has to be increased as well. Additional hardware on the pick-and-place head increases the mass of the pick-and-place head. For high throughput, however, high accelerations are needed, hence, higher mass is undesirable, and besides also increases costs. And in particular when upgrading existing heads with additional nozzles, many parts of the head need to be modified or changed, especially so that the number of vacuum supplies and of vacuum sensors can be increased as required.
While the above has described a typical situation for handling electronic components using vocabulary current in that field, the problem shown in the above example is more general. Wherever large numbers of components or work-pieces, especially components of at least roughly the same geometry, need to be handled during manufacturing, robots, or more generally, pick-and-place devices, may be employed that can pick or place more than one component at once. Using vacuum applied to the work-pieces via nozzles for picking the work-pieces is a widespread concept. For placing a work-piece, or dropping a work-piece from a nozzle, the vacuum for the corresponding nozzle is cancelled, additionally a burst of gas, usually air, may be used to actively blow the work-piece from the nozzle.
As has already been indicated above, if a pick-and-place head is to be modified to change the number of nozzles it exhibits so that the number of work-pieces it can handle at once is changed, in typical pick-and-place heads major reconfigurations are required, as each nozzle has its separate vacuum supply, usually with corresponding vacuum sensor. Furthermore, providing separate vacuum supplies and vacuum sensors for each nozzle renders the configuration of the pick-and-place head quite complex.